With an increasing quantity of user equipments (UE, User Equipment), an existing wireless communications system cannot meet a wireless communication requirement of a user. Therefore, there is an urgent need to increase a system capacity of the wireless communications system. The system capacity may be increased by adding base stations. Typically, many small cells are deployed densely in a macro cell, to form more micro cells. However, most UE is connected to a base station, and the base station provides a wireless communication service for the UE. For brevity of description, a network device that provides a wireless communication service for UE is referred to as a serving node of the UE, and the serving node may be specifically a base station.
In the prior art, when UE is handed over from a cell to another cell, or when UE is handed over from a coverage area of a base station to a coverage area of another base station, or when UE finds a radio link failure (RLF, Radio Link Failure), a serving node handover may be performed on the UE, that is, the serving node of the UE is changed from a base station to another base station. Because the serving node and a mobility management entity (MME, Mobility management entity) are connected by using a control plane interface, and the serving node and a serving gateway (SGW, Serving Gateway) are connected by using a user plane interface, after the serving node handover is performed on the UE, signaling needs to be sent between a new serving node and the MME to update an S1 control plane connection between the serving node and the MME, and signaling also needs to be sent between the MME and the SGW to update an S1 user plane connection between the serving node and the SGW. Therefore, each handover process brings at least four messages. When deployment density of a base station quantity increases, a handover quantity increases sharply, and consequently, signaling load of a core network increases sharply. In addition, each serving node and the MME are connected by using a control plane interface. When the MME has a paging message to be sent, the MME sends the paging message to all base stations in a tracking area (TA, tracking area) area corresponding to the paging message. As a result, signaling load of a core network increases sharply.